Calculate your Body Mass Index for metric or imperial units and see your weight category instantly.
Body Mass Index (BMI) is a number derived from your height and weight that is used as a quick first-pass screening tool to categorise weight status. The formula is simple: weight in kilograms divided by height in metres squared (kg/m²). For imperial measurements the equivalent is (weight in lbs × 703) divided by height in inches squared. This calculator supports both unit systems, does all the arithmetic instantly in your browser, and displays your result on a colour-coded scale so you can see at a glance which category you fall into.
Important: BMI is a population-level screening tool, not a clinical diagnosis. It does not account for muscle mass, bone density, age, sex, or where fat is distributed on the body. A very muscular person may have a "overweight" BMI despite having low body fat. Children and teenagers use age- and sex-specific BMI charts. Always speak with a healthcare professional before making health decisions based on any single measurement.
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Risk of nutritional deficiency |
| 18.5 – 24.9 | Normal weight | Lowest risk range |
| 25.0 – 29.9 | Overweight | Moderate increased risk |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40.0 and above | Obese Class III (Severe) | Extremely high risk |
Reviewed by the ToolBrainy Team · Calculations run entirely in your browser · Last updated July 2026
Click Metric (kg / cm) if you measure in kilograms and centimetres, or Imperial (lbs / ft) if you use pounds and feet. The input fields update accordingly.
For metric, type your height in centimetres (e.g. 175) and weight in kilograms (e.g. 72). For imperial, enter feet and inches separately (e.g. 5 ft 9 in) and weight in pounds.
Click Calculate BMI to see your score and weight category displayed on the colour-coded scale. The marker shows exactly where you land between Underweight, Normal, Overweight, and Obese.
Your measurements never leave your browser.
Works with kg/cm or lbs/ft, your choice.
A clear gauge shows exactly where you fall.
No signup, no limits and no watermarks, ever.
Knowing your starting BMI gives you a baseline to measure progress against. If you are currently in the Overweight category — a BMI between 25 and 29.9 — even modest reductions of 5–10% of body weight are associated with measurable health improvements.
Healthcare providers often note BMI at routine check-ups. Knowing your number beforehand helps you understand where it falls in the standard categories and prepares you for the conversation.
After a few months of consistent exercise or a change in diet, recalculating BMI lets you see whether your efforts are moving your number in the right direction — even if the change is small.
If you know your measurements in one system but a chart or app uses the other, this calculator handles the conversion automatically — useful when reading health materials from countries that use different standards.
A BMI between 18.5 and 24.9 is considered normal weight and is associated with the lowest health risk for the general adult population. Below 18.5 is underweight, 25.0–29.9 is overweight, and 30 or above is classified as obese across three sub-categories. These ranges come from WHO guidelines and are widely used in clinical practice, though they are not diagnostic on their own.
For metric: BMI = weight (kg) ÷ height (m)². So a person who is 175 cm (1.75 m) and weighs 75 kg has a BMI of 75 ÷ (1.75 × 1.75) = 75 ÷ 3.0625 ≈ 24.5. For imperial: BMI = (weight in lbs × 703) ÷ height in inches². This calculator handles both conversions for you.
No — BMI tends to overestimate health risk in heavily muscular people because muscle is denser than fat. A professional athlete may have a BMI in the "overweight" range while having very low body fat. If this applies to you, waist circumference measurements or body fat percentage (via DEXA scan or skinfold calipers) provide a more accurate picture.
Standard adult BMI categories (18.5, 25, 30) do not apply to children and teenagers. For under-18s, BMI is plotted on age- and sex-specific growth charts as a percentile rather than an absolute category. Speak with a paediatrician for guidance on children's weight health.
BMI is a starting point, not a verdict. If your result falls outside the normal range, the most useful next step is to speak with a doctor or registered dietitian. They can assess your full picture — including waist measurement, blood pressure, cholesterol, and activity level — and suggest appropriate action. Small, sustainable changes are generally more effective than rapid interventions.
Yes. All calculations happen in JavaScript in your browser. Your height and weight are never sent to or stored on any server.
Yes, it is completely free with no signup, no limits and no app to install. Calculate your BMI as many times as you like, right in your browser.
The standard adult BMI thresholds (18.5, 25, 30) are the same for men and women. However, at the same BMI women tend to carry more body fat than men, so BMI is best treated as a general screen rather than a precise measure of body composition.